The RiD cast could be from the future (like Beast Wars)
In fact, what if after Beast Machines that era's Megatron somehow survives, takes on a new form (the RiD one, hence the dragon mode), gathers together a new crew of Predacons and makes his way into the past to try and destroy Prime again.
Only he miscalculates and ends up circa 2001, just after the bots and cons have been offlined by the Ark II explosion.
They're followed by the future Autobot leader RiD Prime and his crew back into the past.
They're all gone by the time Lazarus starts resurrecting the G1 Transformers.
The Day of the Doctor - 23.11.13 - #SaveTheDay